Refrigerating machines such as refrigerators, car air-conditioners, room air-conditioners, and automatic vending machines have a compressor for circulating a refrigerant in a refrigeration cycle. The compressor is charged with a refrigerating machine oil for lubricating a sliding part. Thus, the refrigerating machine oil coexists with the refrigerant in the refrigerating machine and, therefore, the refrigerating machine oil is required to have properties such as: lubricity, and thermal and chemical stability, in the presence of the refrigerant; and compatibility with the refrigerant.
For example, Patent Literature 1 discloses a lubricating oil composition for a compression refrigerating machine that exhibits superior thermal and chemical stability even when used in a compression refrigerating machine employing a predetermined saturated hydrofluorocarbon refrigerant, the lubricating oil composition containing a base oil and a predetermined organic compound having a double bond in the molecule.
Meanwhile, the use of unsaturated hydrofluorocarbon refrigerants having very low ozone depletion potential and global warming potential has recently been proposed in view of environmental effects. However, the aforementioned various properties required of a refrigerating machine oil may show unpredictable behaviors depending on the kind of the coexisting refrigerant; thus, a refrigerating machine oil that shows superior properties for use with a saturated hydrofluorocarbon refrigerant, such as the refrigerating machine oil as described in Patent Literature 1, does not necessarily show superior properties for use with an unsaturated hydrofluorocarbon refrigerant.